1. Field of the Invention:
This invention relates to a coil for an electric motor which is attached to a printed circuit board, and more particularly to a coil most suitable for a flat brushless DC motor.
2. Description of the Prior Art:
For example, a coil 1 shown in FIG. 1 is used for a prior flat brushless DC motor. The coil 1 is formed substantially in the shape of a triangle, and it has a substantially triangular opening 1a. Terminal portions 1b and 1c are led out as lead wires. A conductor wire 2 shown in FIG. 2 is used for forming the coil 1. In the conductor wire 2, an insulating film 4, for example, of enamel is formed on a core wire 3 of copper, and an adhesive film 5 is formed on the insulating film 4. This conductor wire 2 is so called "self-bonding wire".
In a flat brushless DC motor, a plurality of the coils 1 are mounted on predetermined positions of a printed circuit board. The lead wires 1b and 1c are soldered to predetermined circuit patterns, or to predetermined terminal pins fixed on the printed circuit board. In the soldering operation, the lead wires 1b and 1c are manually positioned on the predetermined circuit patterns or to the predetermined terminal pins. The soldering operation is very inefficient. When the lead wires 1b and 1c are soldered to the predetermined terminal pins, a special device is required for engaging the lead wires 1b and 1c with the terminal pins. A considerable space is required for introducing the lead wires 1b and 1c from the coil 1, resulting in the electric motors being large. The lead wires 1b and 1c will easily disconnect from the electrical circuit causing open circuits and faults and reducing reliability.
The coil 1 is formed by an automatic winding machine. In the winding operation, the lead wire 1b which is the initial end of the coil 1 contacts with a side surface 1d of the coil 1. The contacting portion is often disorderly wound. It is difficult to orderly wind the coil 1 at high density.